1. Field of the Invention
The present invention relates to a touch sensing system, and more particularly, to a touch sensing system with a passive mode.
2. Description of the Prior Art
Touch sensing interfaces is one of the important human-machine interfaces for electronic systems. They are widely used in many electronic devices, such as smart phones, laptops, Tablet PCs, and the like. Consumer electronic products that are vital to modern life frequently utilize touch panels as the main human-machine interfaces.
It is well known that an electronic system with touch sensing functionality includes a touch area with which the finger(s) of a user or a stylus can make contact. In general, existing touch sensing systems may be resistive, capacitive, optical, surface-acoustic-wave techniques. Among these techniques, capacitive touch control techniques are mostly used in small/medium sized touch screens, and thus becoming the mainstream techniques with large amount of applications in the market.
Referring now to FIG. 1, a smart phone or a tablet device 100 of the prior art is shown. The device 10 includes a housing 110. The main human-machine interfaces on the housing are a touch screen 120 and at least one button 130. The role of the button 130 is limited to turning on/off the device 100 or the touch screen 120. A user operates all the functions of the device 100 through the touch screen 120.
The touch screen 120 using the capacitive touch sensing technique usually includes a touch panel stacked on top of the screen for allowing the user's hand or stylus to make contact with. The touch panel includes a plurality of conducting wires therein. Each conducting wire is coupled to a touch sensing circuit in a touch sensing device.
There are generally two types of capacitive touch sensing techniques: one is called mutual capacitive technique, and the other is called self capacitive technique. Both of these techniques determine the location of a touch point by measuring a voltage drop of a driving voltage as a result of capacitive variation on a conducting wire touched or approached by the finger or stylus. Both of these techniques rely on the touch sensing circuit coupled to the conducting wires to apply a driving voltage. When supplying this driving voltage, the capacitive touch system has to continuously consume power in order to provide the voltage on the conducting wires.
Referring to FIG. 2, a state diagram of a capacitive touch system of the prior art is shown. On a battery-powered mobile device 100, during continuous use, the capacitive touch system has to remain in a driving mode 210. In the state of this driving mode 210, a driving voltage is provided to the conducting wires in the touch area so as to measure the input of the user. In order to conserve power, after an idle period in which no user input is received, or when a user's instruction is received, the electronic device 100 will turn off its touch screen 120, and the capacitive touch system is made to enter into a stop mode 220.
In the stop mode 220, since no driving voltage is provided to the conducting wires in the touch area, the touch sensing system cannot measure any input of the user made in the touch area, but it also saves power used by the touch sensing system otherwise. When the user wishes to wake up the device 100, she/he has to use other input or sensor on the device 100 to do that. One convenient way is to press the button 130, and the device 100 will start up the touch sensing system and return into the state of the driving mode 210.
The design of the button 130 is usually mechanical having a movable part that allows the user to feel the contact pressure. Since the button 130 has a movable part, compared to other components without any movable part in the device 100, the use lifespan of the button 130 may be the shortest. In addition, because the button 130 has a movable part therein, in terms of waterproof and dustproof abilities, it is poorer than other components that are encapsulated by the housing 110. Therefore, the button 130 is the “Achilles' tendon” in the device 100. When the button 130 is faulty, the user may not be able to wake up the device 100 that is in the stop mode 220.
Therefore, if the main input component, that is, the touch screen 120 in the device is able to enter into a more power-saving mode, then it may be possible to eliminate the button 130 from the device 100. Alternatively, if, at least, the number of buttons 130 is minimized, or the frequency of use of the button 130 is minimized, and the device 100 is woken up directly via the touch screen 120, the overall lifespan or mean time between failures can be lengthened. The probability of accidental failure as a result of water or dust permeation can be considerably reduced.